This invention relates to fluid cooled diaphragms for diaphragm compressors of the multi-layer type wherein there are at least two layers that are grooved to provide passageways for cooling fluid circulation.
It is well known that diaphragm compressors must be carefully designed so that the diaphragm does not become overstressed during its excursion between the two carefully contoured plates that are designed to limit the diaphragms combined tensile, bending and other circumferential stresses. What has not been addressed in my prior patents is that the heat removal system must control the thermal expansion of the diaphragm in the central region, where it is in contact with the gas. This area is where the cavities in the gas and/or liquid support heads are contoured to keep the diaphragm from being overstressed in its motion in compressing the gas. The heat of compression is usually polytropic in nature. At slow speeds, compression approaches isothermal, but as the speed is increased, adiabatic conditions are approached.
This heat quickly makes the inner portion of the diaphragm longer than the cooler outer clamped portion. For example, if the center portion of the diaphragm on a 10xe2x80x3 cavity becomes 100 degrees Fahrenheit hotter than the outer rim, the thermal expansion will cause the center portion to become 0.0096xe2x80x3 longer if the rate of thermal expansion of 302 stainless steel is 0.0000096 inches/inch/degrees Fahrenheit. This causes the diaphragm to become bowed and to xe2x80x9csnapxe2x80x9d when it moves through the center of its travel. The bottom of an old style oil can also does this when it snaps between its two positions. The stresses imposed on the diaphragm can possibly be calculated, if the temperatures at all the points on the diaphragm were known, however experience has shown that it this is very difficult to predict, and it is well known that the life of the diaphragm is materially affected by these temperature variations. The denser the inlet gas is and/or the greater the speed of the compressor the more heat is generated in the cavity during the compression cycle in a given amount of time. This heat must be dissipated or the retaining heads and the diaphragm will become quite hot. For example, air compressed from 1000 psig inlet to 5000 psig outlet will theoretically rise in temperature from 72 degrees Fahrenheit to 382 degrees Fahrenheit. This rise does not happen because heat is lost through the head and the diaphragm, however, it does show the potential rise. If this heat is not removed via the head or the diaphragm, these parts will approach this temperature over time when steady state conditions are established.
In general there has been a tendency to run this type of compressor at faster speeds. This means that more energy must be lost per unit time. Discharge temperatures approaching adiabatic are starting to be realized.
To stretch the 10 inch diaphragm 0.0096xe2x80x3, the tensile stress would have to be (29,600,000)*(0.0096)/(10)=28,416 psi. This is about the stress level that is used for design purposes for the tensile stresses. This effectively reduces the tensile stress to zero a t the extreme ends of the motion of the diaphragm, but when the diaphragm moves to the center of its motion, this becomes a compressive stress. Since the thickness of the diaphragm is small compared to its width, buckling occurs. The diaphragm therefore snaps through the mid point. Stresses however are not easily predicted, because the inlet gas cools the diaphragm near its normal off-center location. The diaphragm therefore is not of a uniform temperature. This makes exact prediction of the movement and the attendant stresses difficult.
Various cooling arrangements have been proposed for diaphragm construction such as shown in U.S. Pat. Nos. 4,621,989; 4,636,149; 3,650,639; 3,877,842; and 4,710,109 but none of them provides a satisfactory solution to the problem with metal diaphragms.
The solution to this problem is overcome by removing the heat as quickly as can be done with the given materials of construction.
In my U.S. Pat. Nos. 3,661,060 and 3,668,978, coatings were employed to provide heat insulation properties and protection against fretting corrosion. This technique works for small compressors at low speeds. At higher ( greater than 300 RPM) speeds, the problem becomes more difficult as there is less and less time to get rid of a greater amount of heat generated from the larger gas mass flow.
My invention provides cooling passages underneath the primary or gas contacting diaphragm layer for cooling fluid circulation.
This invention relates to fluid cooled diaphragms for diaphragm compressors which diaphragms are of multi-layer construction with the middle layer having grooves for cooling fluid circulation.
The principal object of the invention is to provide fluid cooled diaphragms for diaphragm compressors.
A further object of the invention is to provide diaphragms of at least two or more layers of construction.
A further object of the invention is to provide diaphragms of multi-layer construction where the layers may be loose, or only partially bonded as well as fully bonded to the gas contacting layer.
A further object of the invention is to provide diaphragms which have an improved service life.
Other objects and advantageous features of the invention will be apparent from the description and claims.